Three major auto manufacturers are promising to reserve 300 new hybrid vehicles each month exclusively for the city as it replaces its entire fleet of yellow cabs.

Nissan North America, General Motors and the Ford Motor Co. said Wednesday that they are setting aside the environmentally friendly cars to help the city reach its goal of making all yellow cabs green by 2012. Today there are about 13,000 cabs on the street and more than 1,300 are hybrids.

New city regulations require that any new cab coming into service after Oct. 1, 2008, achieve a fuel efficiency standard of 25 miles per gallon. The following year, that increases to 30 miles per gallon.

The standard yellow cab in use today, the Ford Crown Victoria, gets about 14 miles per gallon. But some hybrid models, which run on a combination of gasoline and electricity, achieve as much as 36.

The government does not own the city's yellow cabs, but sells licenses to drivers and operators, who must purchase vehicles that meet the specifications of the Taxi and Limousine Commission. The agency regulates and licenses all for-hire vehicles in the city.

Some taxi fleet owners had recently complained to Mayor Michael Bloomberg's administration that there would not be enough hybrids available on the market for all drivers to meet the city's fuel efficiency regulations by the deadline.

Bloomberg said the help from the auto companies guarantees that won't be a problem.

"We want to ensure there is more than enough supply to meet the demand for hybrid taxis," Bloomberg said in a statement.

At least one fleet owner said Wednesday that there was not enough research yet about how safely hybrids can perform as taxi cabs, which can clock tens of thousands of miles each year and are on the road for longer lengths of time than regular cars.

Ron Sherman, of the Metropolitan Taxicab Board of Trade, said the city "is asking taxi passengers and taxi drivers to become human crash test dummies."

Bloomberg, when asked about the safety issue at a news conference later Wednesday, said every study the city has examined says hybrids are safe for use as cabs. He suggested that dirty exhaust from standard cabs poses more of a safety hazard.

"Maybe that's not what you should be worrying about — try the air that you're breathing when they go by," he said.

Both the city and taxi driver advocacy groups acknowledge that drivers or fleet owners will have to spend more money up front when purchasing hybrid vehicles, but point out that they will save money on fuel. The Taxi and Limousine Commission estimates that a hybrid cab saves a driver $6,500 per year.

The life of a city taxi is typically about three to five years because the commission requires all vehicles to be retired within a certain time frame.